Various systems for forming an image have been adopted in an image forming apparatus, which forms images on a recording medium such as a sheet of paper, in order to reduce the size of the apparatus and increase the processing speed of the apparatus. For example, there are known systems for forming an image such as: an electrophotographic system that visualizes an electrostatic latent image formed on a photoreceptor drum by using a toner; an inkjet system that forms an image by directly discharging ink drops on the recording medium; and a silver salt photographic system that exposes a recorded image to a photoconductive dye.
In the various systems for forming an image, for example, after a sheet is fed from a sheet cassette or a manual feeding tray and positioned by registration rollers while being conveyed by a conveying device, the sheet is supplied to an image forming position. When the sheet is supplied to the image forming position, operation noises, such as driving noises of a feed roller and a conveying roller or an impact noise caused by the bump of the sheet against the registration rollers are generated.
In order to reduce the operation noises generated during supplying the sheets, there is proposed an apparatus that feeds the sheet from a cassette closest to an image forming device. See JP-A-2004-167798 for an example of such conventional sheet conveying device.
However, noises generated during supplying the sheets are caused by various factors, like impact noises that are due to the change of loads caused by sudden operation of the feed roller or the conveying roller from stopped state or impact noises that are caused by the impact of the sheets against the registration rollers. In particular, when images are consecutively formed, different kinds of sounds are continuously generated at several positions on a sheet conveyance path.
Meanwhile, the image forming apparatus is generally installed in an office. It is preferable that the operation noises of the apparatus would be fairly less under the office environment, and a sound pressure level of the operation sound is set as a product specification. However, even though the sound pressure level of the operation sound satisfies the product specification, there is a concern that the character of the operation sound of the apparatus deteriorates due to the impact noises related with the supply of the sheets.
For example, in a copy machine that prints sixty sheets per one minute, one sheet is conveyed per one second and images are then formed on the sheet. Further, while one sheet is conveyed, several impact noises, which are represented by onomatopoeic words of “click-click-tum-tum” or “tick-tick-pat-pat”, are randomly generated per one second from several noise sources. There is a problem in that the above-mentioned operation noises are frequent and cause a user an uncomfortable feeling.